In this work, a novel characterization technique taking advantage of the maturity and high sensitivity of Fourier domain optical coherence tomography (FD-OCT). The method has been experimentally verified on a silicon photonic chip fabricated using imec-ePIXfab passive technology with a waveguide height and width of 220 nm and 500 nm, respectively. The silicon is surrounded by air from top and by silicon-oxide from bottom and sides. The design assumes quasi Transverse Magnetic (TM) mode with an effective refractive index neff of 1.61 and group effective refractive index ng of about 3.471 at 1550 nm. The method is applied on a simple 1.46 mm length waveguide ended by grating couplers from both sides. Using that length and by inspecting the spatial response obtained after inverse Fast Fourier Transformation (FFT), the extracted mean group effective refractive index ng of the straight waveguide is 3.597. This value is attributed to the fabrication tolerance in the width of the structure leading to a width error of about 7.7 %.
In this work, we present the realization of a novel configuration of dual-coupler nested coupled ring resonator on silicon photonics technology. The waveguide height and width are 220 nm and 500 nm, respectively, surrounded by air from the top and by silicon-oxide on the three other sides. The design assumes TM mode with group refractive index of 3.17 at 1550 nm. The design consists of two mini-racetrack resonators of the smallest lengths of 150.8 and 182.13 μm corresponding to resonance, and bending radius of 25 μm, to minimize bending losses. The directional couplers are designed for a coupling ratio of 97/3. The proposed configuration and the single cavity ring resonator are fabricated using IMEC- ePIXfab passive technology. The measured response shows that the new configuration enhances the finesse by up to 10 times. The proposed high finesse resonator can boost the performance in many applications such as gas sensing, rotation sensing and optical filters.